Centers controlling microtubule distribution in eukaryotic cells undergo orderly transitions during the cell cycle-the complex cytoskeleton giving way to the mitotic spindle as the cell enters mitosis and then being reformed at interphase. The mechanisms of these crucial transitions of microtubule organization are poorly understood in most eukaryotes but are amenable to analysis in the yeast, Saccharomyces cervisiae, where microtubule distribution is centered on the discrete spindle pole bodies and genetic analysis is straight-forward. Genetic and cytological analysis has identified certian cell division cycle (CDC) genes as being required during spindle pole body duplication and separation as the cell forms the mitotic spindle and enters the mitotic cycle. We intend to gain a better understanding of this transition by isolating and characterizing additional genetic variants and by applying molecular cloning techniques to the characterization of these genes and their products during mitosis and meiosis. Biochemical and immunological studies of isolated spindle pole bodies will provide a basis for determining correlated molecular mechanisms. The value of genetic analysis is critical to the choice of yeast for this work, as is the facility for cloning genes by functional complementation of mutant alleles. The understanding gained by these powerful techniques may prove useful in designing methods for determining how microtubule organizatin and the cell cycle are controlled in normal and abnormal human tissues.